1. Field of the Invention
The present invention relates to an SOI (silicon on insulator) substrate and a manufacturing method thereof. Further, the present invention relates to a semiconductor device formed using the SOI substrate and a manufacturing method thereof.
2. Description of the Related Art
In recent years, integrated circuits using an SOI (silicon on insulator) substrate in which a thin single crystal semiconductor layer is provided over an insulating surface instead of a bulk silicon wafer have been developed. Transistors in an integrated circuit can be formed so as to be completely separated from each other by making the most of characteristics of a thin single crystal silicon film formed over an insulating surface. Further, since the transistors can be formed as fully depleted transistors, a semiconductor integrated circuit having high added value such as high integration, high-speed driving, and low power consumption can be realized.
One of methods for manufacturing SOI substrates is a Smart Cut (registered trademark) method. By a Smart Cut method, not only an SOI substrate in which a single crystal silicon film is formed over a silicon substrate but also an SOI substrate in which a single crystal silicon film is formed over an insulating substrate such as a glass substrate can be manufactured (for example, see Patent Document 1). The outline of the method for manufacturing an SOI substrate in which a thin single crystal silicon film is formed over a glass substrate using a Smart Cut method is as follows. First, a silicon dioxide film is formed over one surface of a piece of single crystal silicon. Next, hydrogen ions are added to the piece of single crystal silicon, whereby a hydrogen-ion-introduced layer is formed at a predetermined depth of the piece of single crystal silicon. Then, the piece of single crystal silicon to which hydrogen ions are added is bonded to a glass substrate with the silicon dioxide film interposed therebetween. After that, heat treatment is performed, whereby the hydrogen-ion-introduced layer functions as a cleavage plane and then the piece of single crystal silicon to which hydrogen ions are added is thinly separated. In this manner, a thin single crystal silicon film can be formed over the glass substrate to which the piece of single crystal silicon is bonded. A Smart Cut (registered trademark) method may be referred to as a hydrogen-ion-implantation-separation method.